The present invention relates to a rubber composition capable of producing a golf ball which provides good shot feeling and extended durability, and a golf ball such as a one-piece golf ball, a two-piece golf ball, and a multi-piece golf ball produced using the same.
Commercial golf balls fall into two broad categories: thread-wound golf balls and solid golf balls. The commercial solid golf balls fall into two categories: one-piece solid golf balls and two-piece golf balls. A one-piece solid golf ball has a single-layered structure of a vulcanized rubber composition. A two-piece golf ball has a two-layered structure of a core and a cover. The core has a single-layered structure of a vulcanized rubber composition, and is covered with the cover having a single-layered structure.
The solid golf ball is superior to the thread-wound golf ball in resilience and flight distance. However, the solid golf ball has a problem that it produces hard and bad shot feeling when hit.
In order to solve the problem of bad shot feeling that the two-piece golf ball has, there have been developed a new type of two-piece solid golf ball called "a soft two-piece golf ball", and a multi-piece golf ball having three or more layered structure. The multi-piece golf ball has three or more layered structure of a core and a cover. The core has one or more layered structure of a vulcanized rubber composition, and is covered with the cover having two or more layered structure.
The soft two-piece golf ball and the multi-piece golf ball produce soft shot feeling when hit, because the difference in hardness between the center and the periphery of the core is made to be large. However, the large difference in hardness between the periphery and the center of the core lowers the durability of the golf ball. As a result, the golf ball is likely to break, and there is a case where it breaks after being hit less than thirty times with a golf club which produces large impact such as a driver.
In order to solve the above-described problem and to improve the durability of the golf ball, Japanese Unexamined Patent Application No. 6-7481 suggests to add vulcanized rubber powder to the rubber composition for the core. However, in this prior art, large amount of the vulcanized rubber powder is added to the rubber composition, and therefore, only small amount of unvulcanized lubber component is contained. The large amount of the vulcanized rubber powder increases the hardness of the core, and the resultant golf ball becomes hard and produces bad shot feeling. Furthermore, the rubber composition containing the large amount of the vulcanized rubber powder cannot be smoothly kneaded, and lowers the workability of the golf ball production.
A one-piece golf ball also has a problem as follows. That is, a one-piece solid golf ball is used at a golf practice range in many cases. Accordingly, the main requirement for the one-piece golf ball is high durability such that it never breaks even when repeatedly hit, rather than good shot feeling. Recently, there has been a remarkable progress in golf club technology, and the golf club gives large impact to the golf ball. The conventional solid golf ball is unable to resist such large impact.